A clamping device of this kind is disclosed in EP 15 150 064. In order to undertake both internal and external clamping by means of the power-operated chuck, in this embodiment several spring packs forming the force accumulator are arranged evenly around the circumference on both sides of pressure pieces acting on the adjustment element of the motion converter. In this case, although the springs are guided on pins screwed into the housing and are alternately clamped by the axial movement of the pressure piece, a defined preload of the springs that are not involved in the particular clamping procedure is not provided. Instead, these springs have the force removed from them and are held with axial play in holes worked in the pressure piece, which as a result of the holes having a diameter larger than the springs, are not suitable for guidance purposes.
Apart from the fact that this means two force accumulators with a large number of spring packs are required for both clamping directions, the axial play on the force accumulator which is not loaded means that when the clamping direction is reversed there is the requirement for this clearance to be crossed before any clamping force can be established. The adjustment range to be specified for the motion converter must consequently be made relatively large, and also it is necessary to cover a dead travel before clamping force is established. Despite the significant constructional complexity, this means that a satisfactory operating method is not provided. Furthermore, it is a disadvantage that a defined middle position of the pressure piece cannot be achieved because during a clamping procedure, a signal is only available and able to be evaluated once an adjustment movement of the pressure piece to which a signal ring is attached takes place.